In a communications system, some devices have clock synchronization requirements, for example, in a wireless bearer network, it is required that a radio base station is provided with a synchronous clock reference source; when a soft handover is performed between radio base stations, if clock synchronization is not performed between a radio network controller (RNC) and a base station (e.g., a NodeB), a call may not be able to be established, and time and frequency deviations further affect a handover success rate of a mobile station (MS) between base stations.
In the prior art, clock synchronization between networks is implemented based on an Institute of Electrical and Electronics Engineers (IEEE) 1588V2 protocol; in the solution, a time source is acquired by means of a global positioning system (GPS) and the like, and a bearer device transmits time information through the 1588V2 protocol, a base station acquires the time information from the bearer device so as to achieve a purpose of synchronizing with the time source; the bearer device as a clock server may be a standalone device, and may also be integrated in a device such as a router.
However, with the development of a communications network, a network device in an existing network architecture also adopts an Internet Protocol (IP) protocol to exchange a clock synchronization message with a clock server based on the 1588V2 protocol. The IP protocol is connectionless; therefore, there may be multiple paths between a device with a clock synchronization requirement and a clock server, and especially, when the device and the clock server cross different types of networks, for example, physical media of networks where the device and the clock server are located are different, one is an Ethernet and the other is an optical switching network; or the device and the clock server belong to different operators or belong to different operating services of the same operator; in these situations, the device with the clock synchronization requirement and the clock server may transmit a packet through different paths, and therefore an error occurs during clock synchronization.